[Elecraft] Mic Problem?

[Don Wilhelm]

Ken,

Wow, a quick perusal of your connections sounds like you may have ground
loop potentials galore in that hookup.  I will digest your notes better in
the morning, but at a minimum, yes, you should ground the mic jack.

The directions for grounding the mic jack are around the web somewhere
(might check the Elecraft website), but it is really easy - remove the front
panel and then extract the front panel board (remove knobs, encoder nut and
the screw next to the encoder).  When you have the mic connector sitting
'bare' on the front panel board, wrap a wire around the mic jack and solder
that wire to the jack (takes a LOT of heat), then ground that wire to the
nearby grounding point on the PC board.

If you want to (or need to) do an even better job of it, also run a short
piece of braid from the ground point/mic jack wire to the chassis 2-D
connector and pinch the wire against the chassis when the front panel is
assembled to provide a direct path for any common mode currents on the mic
cable shield direct to the chassis of the K2 rather than relying on a
circuitous path through the PC board somewhere to the chassis (this is
referred to in audio circles as the "pin 1 problem" - I give Jim Brown
credit for that one).

Try grounding the mic jack - it may not cure everything, but it certainly
will do no harm.

One other thing - be certain you have not connected the PC serial port pin 1
to the shield at the computer end of the K2 to PC cable.  Pin 1 at the PC
end is Data Carrier Detect, and pin 1 at the K2 end is chassis ground - the
two do not match.  The computer chassis ground is the shell of the DB9
connector, not pin 1.  The recent discussion of this 'RS232' situation under
the subject of the 'microHam keyer' interface may be relevant in your case.

73,
Don W3FPR


        -------Original Message-------


        Thanks, Don - I did some tests with the help of KB0OMQ/M
        this evening and discovered several things:

        1) No matter what I do, I cannot get the PTT with one
             glaring exception - it works FB if I hook up my PC!
        2) VOX works, provided I hit the PTT to switch in the
             mic element.
        3) The transmitted audio sounds better either at 5w or
             less *or* when on my R7000 vertical. My other antenna
             is a coax/choke/ladder line fed 40m inverted V @ 40'

        The computer PTT is very simple - COM 2 is the radio
        and COM 1 goes to a 1 transistor PTT to ground
        switch. The output of this switch, along with the audio
        lines, go to a mic connector with a pigtail going to the
        speaker jack. Pretty standard stuff but it is an entirely
        seperate PTT control than the mic.

        I just did a test - I opened the mic up and used a test
        lead to bypass the ground from the PTT switch to the
        mic connector. Nothing. Then I had an idea - I tried the
        same trick but used the shell of the *computer* mic plug
        with that *unhooked* from the radio. It worked!

        I then tried touching the bypass lead to a case screw.
        Works perfectly.

        I thought the case of the mic jack was grounded to the
        chassis? Should it be? Mine's not.

        I'll take the rig apart and check for a poor ground for
        the mic..... I know I'm close - betcha it's something stupid,
        eh?

            73 de Ken KGØWX - Flying Pigs #-1055
        Elecraft K2 #4913 - Kadiddlehoppers #11,808